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module 9 Flashcards

cell signalling (65 cards)

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1
Q

what is cell signalling

A

transferring info from the outside of the cell to obtain a response inside the cell

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2
Q

how do cells communicate

A

by sending and receiving chemical signals that can take place over short/long distances

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3
Q

what are the essential elements to communication between cells

A
  1. signalling cell
  2. signalling molecule
  3. receptor molecule
  4. receptor cell
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4
Q

how do bacteria cells signal to take up DNA from the environment?

A

a small peptide is continuously synthesized by pneumococcal bacterial cells

cells express a receptor for this peptide on surface

when peptide binds to receptor, bacterium expresses genes that enable it to take up DNA from the environment

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5
Q

what happens if there is a LOW density of bacteria? do the bacteria still take up DNA

A

low peptide levels

signal falls below critical threshold

gene expression is turned off

signalling peptide is too low to bind to receptors and stimulate DNA uptake

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6
Q

what happens if there is a HIGH density of bacteria? do the bacteria still take up DNA

A

high peptide levels

peptide is bound and signal is relayed by signal transduction to nucleoid region

genes that prod proteins involved in DNA uptake from environment are turned on

concentration of signalling peptide is high enough to bind to receptors -> stim DNA uptake

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7
Q

what 4 elements do cells within a multicellular organism need to communicate

A
  1. signalling cell (cells of adrenal glands)
  2. signalling molecule (release of epinephrine)
  3. receptor protein (found on cells of target organs)
  4. responding cell (changes in physiological function, ex. incr. heart rate)
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8
Q

what are the 4 steps involved in signalling between cells

A
  1. receptor activation: binding of signalling molecule
  2. signal transduction: transmission of signal into cell
  3. cellular response: specific for the target cell
  4. signal termination: stop response
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9
Q

what are ligands

A

receptors that are cell surface proteins that recognize specific molecules

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10
Q

what is the term for when the receptor on the responding cell is turned on?

A

activated

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10
Q

what are the 2 kinds of ligands

A

can be an extracellular ligand (molecules secreted by cells)

can be due to cell-to-cell contact or contact with extracellular matrix

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11
Q

when cell receptors are found inside the cell, how does receptor activation work?

A

ligand travels into cell to bind to receptor

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12
Q

how is the ligand and ligand-binding interaction similar to enzymes?

A

when the ligand binds to the site, a conformational change in the receptor triggers chemical reactions within the cytosol

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13
Q

what is the message that a receptor transmits to the cell through the cytoplasm

A

signal transduction

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14
Q

where does the signal transduction go?

A

can stay in the cytosol or go to the nucleus

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14
Q

what are potential responses to the signal transduction

A

activate enzymes, turn on genes, signal other cells, cause the cell to divide/change shape

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14
Q

what is endocrine signalling

A

long distance communication where the signalling molecules travel thru the bloodstream

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15
Q

what happens once the signal transduction has been sent

A

a series of distinct proteins that are activated/inactivated in a particular sequence

signalling is also frequently amplified, which allows the signal to be transmitted throughout the cell quicker and more instantaneously

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16
Q

once the signal transduction has been received and acted upon, it is _____________

A

terminated!

this stops the cellular response

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16
Q

what is the signal transduction

A

transmits the reception of ligand binding to the receptor the stimulus

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17
Q

what are the classifications of cell communication based on distance?

A

long distance and short distance

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18
Q

how does the signalling molecule move for paracrine signalling? what kind of molecule is it? how far does it travel typically?

A

moves via diffusion

typically small water soluble molecules

travel within a range of ~20 cells

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18
Q

how does endocrine signalling work?

A

target cell expresses the appropriate receptor for the hormone

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18
Q

what chemical signalling molecules do endocrine signalling cells use? what produces them?

A

hormones

produced by endocrine cells

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19
what is paracrine signalling?
neighbouring cells communicate where the signalling molecule travels a short distance
19
what is autocrine signalling
when a cell that secretes a signalling molecule is also the target cell
20
at what stage are paracrine and autocrine signalling significant to multicellular organisms?
during embryonic development
21
what is contact dependent signalling?
occurs because of direct contact between neighbouring cells
22
what is an example of endocrine signalling?
growth hormone
23
what is an example of paracrine signalling
growth factors
24
what is an example of autocrine signalling
interleukin-1
25
how does contact dependent signalling work?
signalling molecule: transmembrane protein on surface of one cell receptor: a transmembrane protein on an adjacent cell
26
what is contact dependent signalling also referred to?
juxtacrine signalling
27
what is an example of contact dependent signalling
notch signalling in embryonic development
28
what is a intracellular receptor
nonpolar signalling molecules can pass through the hydrophobic core of the cell membrane and activate cytoplasmic receptors
29
what is unique about intracellular receptors
do not need a receptor on the outside of the cell
30
what are cell surface receptors
signalling molecules that are polar cannot cross the cell membrane
31
how do cell surface receptors work
bind to transmembrane proteins that are cell-surface receptors binding of ligand to the cell-surface receptors -> change in conformation, activating the receptor
32
how are proteins that take part in cell signalling classified?
1. G protein-coupled receptors -> GPCRs 2. receptor kinases 3. ion channels
33
what kind of organisms are GPCRs found in
virtually every eukaryotic organism
34
why are G proteins-coupled receptors (GPCRs) called GPCRs?
they associate with G proteins: bind to GTP and GDP in the cytoplasm
35
what are the 3 subunits of G proteins
1. alpha (α) part of the G protein that binds to either GDP or GTP 2. beta (β) 3. gamma (γ) when alpha subunit is bound to GDP, 3 subunits are joined
36
how is G protein activity regulated
binding of G protein to GTP or GDP
37
when is a G protein active
when bound to GTP GDP bound is replaced by GTP, leading to separation of alpha subunit from beta and gamma
38
when is a G protein inactive
when bound to GDP 3 subunits join together
39
what happens when a ligand binds to a gpcr?
inactive until a ligand binds to receptor activates the G protein by replacing GDP with GTP if bound to GTP, the G protein is "on", signal continues to be transmitted
40
what happens to G proteins once the GCPRs are activated
GDP is replaced with GTP alpha subunit disassociates from other subunits binds to target proteint o activate the protein
41
what si the difference between a gpcr and a g protein
gpcr acts as surface sensor (receiver) g protein acts as relay switches gpcr needs to be activated before g protein can do its job (as the gpcr disassociates the GDP from the inactive protein, allowing GTP to bind and activate it)
41
explain GPCR activation in heart rate
heart rate can be influenced by signals that activate via a gpcr system thru epinephrine released thru adrenal gland epinephrine aka adrenaline when epinephrine binds to a gpcr on heart muscle, activates G protein GDP on alpha subunit is exchanged with GTP alpha subunit then binds to and activates enzyme adenylyl cyclase in cell membrane converts ATP into signalling molecule cyclic AMP (cAMP) cAMP binds/activates another enzyme, protein kinase A (PKA) activated PKA phosphorylates proteins in the heart, increasing rate of contraction as long as epi is bound to receptor, heart rate will remain high activated adenylyl cyclase converts ATP into second messenger cAMP, which activates protein kinase A kinase A then phosphorylates proteins in heart muscle, causing heart rate to increase
42
what are kinases
enzymes that phosphorylate target proteins
43
signals produced by activated gpcrs are ___________. this means ________________
amplified small amnt of ligand can produce large response
44
explain signal amplification in epinephrine example
3 places: 1. each epinephrine-bound receptor activates multiple G proteins 2. each adenylyl cyclase molecule produces large amnts of cAMP 3. each active PKA activates multiple protein targets
44
what is binding affinity
time a ligand is bound to its receptor depends on how tightly the receptor holds on to it
45
explain binding affinity in epinephrine example
epinephrine leaves receptor, which reverts to inactive conformation -> no longer activates G proteins G proteins convert GTP to GDP -> becoming inactive inactivates adenylyl cyclase -> no more cAMP enzymes in the cytosol degrade cAMP -> stops activation of more protein kinase A molecules phosphates remove phosphate grps from activated proteins -> inactivates proteins
45
what are phosphatases
enzymes that dephosphorylate target proteins
46
when does a receptor kinase become active and what happens
when ligand binds dimerization occurs results in phosphorylation of a another protein, transmitting the signal from outside cell to inside the cell phosphate grps provide binding sites for intracellular signalling proteins
47
dimerization
when receptor kinase receptors associate into dimers
48
examples of receptor kinase use
formation/elongation of structures called limb buds that become arms/legs insulin signalling, allowing us to transport glucose across the plasma membrane into cytosol wound healing -> after paper cut
49
explain process of wound healing with receptor kinases
when blood encounters damaged area, platelets in blood release proteins (platelet derived growth factor) PDGF repair is stimulated by PDGF -> binds to PDGF receptor kinases on the surtface of the cell receptors dimerize and become active phosphorylated receptors help activate other proteins in the cell in MAP kinase pathway, cytoplasmic signalling protein activated is Ras GTP bound Ras triggers a kinase cascade at the end of the cascade, activated kinase enters the nucleus turns on expression of genes associated with cell division pathway is terminated when GTP is replaced by GDP on Ras
50
MAP in context of kinase pathway
mitogen-activated protein
51
what is a kinase cascade
sequential protein phosphorylation and activation of cascade parts
52
ion channels can change the flow of ions across the cell membrane either into ______ or out of _______ the cell
influx, efflux
53
what are the kind of ways ion channels can be gated
1. ligand gated -> respond to binding of a signalling molecule 2. voltage gated -> respond to changes of voltage in the cell 3. mechanically gated -> respond to force applied to the cell
54
the gate is _______ when the movement of the ion is prevented
closed
55
the gate is _______ when the movement of the ion is allowed
open
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